Patent Literature 1 describes “providing Pc cut valves that cut output lines of pressure controlling valves and a connecting valve that connects left and right wheel cylinders, and in an event of failure, the Pc cut valve in a failed system is closed and the connecting valve is opened to send outputs from the pressure controlling valve in a normal system to the wheel cylinder in the failed system”.
Patent Literature 2 describes, an electrically driven fluid pressure output part which is “provided with a cylinder body having its distal end side formed as a closed end to have a bottomed cylinder shape, a guide cylinder coaxially connected to a rear end of the cylinder body, a support cylinder coaxially connected to the guide cylinder, a connecting cylinder coaxially connected to the support cylinder, a motor including an encoder and being coaxially coupled to the connecting cylinder, a piston slidably fitted in the cylinder body and forming a pressure chamber with the closed end of the cylinder body, a cylindrical nut member arranged in the guide cylinder by being prohibited to rotate about an axis line, and coaxially connected to a rear end of the piston, and a rotation shaft coupled to the nut member via a ball screw and connected to an output shaft of the motor via an Oldham's joint (see FIG. 2 of Patent Literature 2)”.
Application of the technical contents described in Patent Literature 1 to the device described in Patent Literature 2 will be assumed. In the device of the Patent Literature 2, since brake fluid is pushed out from the cylinder by the piston, there is a limit to an amount of the brake fluid that can be discharged from the cylinder. Due to this, when the brake fluid is to be supplied from a brake system (fluid path) in a suitable state to a wheel cylinder in a brake system (fluid path) in an unsuitable state, a state in which the piston fully strokes, and the brake fluid can no further be discharged from the cylinder may occur. A so-called piston bottoming occurs, and insufficiency in a brake fluid volume may occur.